DNA encoding SPA-1protein

ABSTRACT

A cell division mechanism controlling protein which is not expressed in the interphase but is expressed in the nucleus after entering into a cell cycle, in the cell cycle of mammalian cell, and fragments thereof, as well as DNAs coding for said protein or fragments thereof, as well as antibodies against said protein or fragment thereof.

CROSS REFERENCE TO RELATED APPLICATION

This application is a division, of application Ser. No. 08/380,403, filed Jan. 30, 1995, now U.S. Pat. No. 5,831,024, which is a continuation-in-part of application Ser. No. 08/325,909, filed Oct. 19, 1994, now abandoned.

TECHNICAL FIELD

The present invention relates to a SPA-1 protein involved in the control of cell division, and fragments thereof, genes coding therefor as well as antibodies against the protein.

BACKGROUND OF INVENTION

Lymphoid cells have unique properties in cell growth ability in comparison with many other somatic cells. Namely, lymphoid cells, similar to many other somatic cells, are differentiated from a hematopoietic stem cell to mature cells via many steps of cell division, and once enter the interphase (G0/G1). After that if they are stimulated with an antigen or a special growth factor, they again enter to a cell cycle and increase to a clone with a redifferentiation, and then return to the interphase (memory cells). In addition to functional differentiation and expression specific to lymphoid cells, such repeated cell proliferation (clone proliferation) is one of the big factors in an immune response of an organism.

DISCLOSURE OF THE INVENTION

The present invention relates to a novel protein SPA-1 and fragments thereof expected to be involved in the control of said repeated cell growth, and fragments thereof, genes coding therefor, as well as antibodies against said proteins.

BRIEF EXPLANATION OF DRAWINGS

FIG. 1 compares an amino acid sequence of Span-N (SEQ ID No:6) and an amino acid sequence of GAP3m protein (SEQ ID NO:7).

FIG. 2 schematically shows a structure of SPA-1 protein.

FIG. 3 shows a process for construction of a recombinant expression plasmid for SPA-1 protein.

FIG. 4 is a graph showing that Span-N activates Ran1 GTPase in a dose dependent manner.

FIG. 5 is a graph showing that Span-N activates Rsrl GTPase in a dose dependent manner.

FIG. 6 shows a restriction enzyme map of a genomic DNA coding for SPA-1 of the present invention.

FIG. 7 shows a result of an electrophoresis showing the reactivity of monoclonal antibodies F6 and H10 to GST protein, GST-Span N and GST-Span C fusion proteins.

FIG. 8 shows a result of an electrophoresis showing a profile of expression products from SPA-1 genes lacking various regions.

FIGS. 9a and 9 b are micrographs showing the effects of the overexpression of SPA-1 gene in an animal cells on the cell growth when the growth of said animal cells is synchronized by serum-starvation and addition of serum.

FIGS. 10a, b and c are micrograph showing the effects of overexpression of a SPA-1 gene introduced into animal cells on the cell growth when the growth of said animal cells is synchronized by serum-starvation and addition of serum.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a protein which controls a mechanism of cell division and is not expressed in the interphase but is a expressed in the nucleus after entering into a cell cycle, during the cell cycle of a mammalian cell.

This protein is designated SPA-1 and has a structure shown in FIG. 2. Namely SPA-1 comprises the N-terminal half thereof which may be further divided to Span-N positioned on the N-terminal side and having a high homology with GAP3 protein, and Span-C adjacent to the C-terminal of the Span-N and having a unique amino acid sequence.

An amino acid sequence deduced from a nucleotide sequence of cDNA starts with the first Met and ends at the 693rd Ala in SEQ ID NO.: 2. The Span-N has an amino acid sequence starting with the first Met and ends with the 190th Leu, and Span-C has an amino acid sequence starting with the 191st Ala and ends at the 327th Leu of SEQ ID NO: 2.

However, polypeptides and proteins of the present invention are not limited to those described above, but those having small modification in a precise amino acid sequence while maintaining the activities of the present invention are included in the present invention. These modifications include replacement of one or more amino acids in the sequence with other amino acids, and addition or deletion of one or more amino acids, and these variations are included in the present invention as far as they maintain the activities of the present invention.

The addition, deletion and replacement of amino acids can be carried out according to site-specific mutagenesis well known prior to filing the present invention (for example, see Nucleic Acid Research Vol. 10, No. 20, p 6487 to 6500, 1982)), and regarding the addition, deletion and replacement of amino acids, “one or more amino acids” means, for example, those number of amino acids which can be added, deleted or replaced by site-directed mutagenesis.

The above-mentioned polypeptides or proteins can be produced by expressing a gene coding for said polypeptides or proteins according to a genetic engineering procedure. A gene coding for said polypeptides or proteins can be obtained as cDNA, genomic DNA or chemically synthesized DNA.

A cDNA coding for SPA-1 may be obtained from lymphocytes by cloning a gene which is not substantially expressed in the interphase (G0/G1 phase) but is expressed in the growth phase (S phase). For example, cDNA coding for SPA-1 can be obtained by preparing a cDNA preparation from lymphocytes in the G0/G1 phase and a cDNA preparation from lymphocytes in the S phase according to a conventional procedure, allowing these cDNA preparations to hybridize, and selecting cDNA from the S phase, which does not hybridize with cDNAs from the G0/G1 phase. An example of the concrete methods for cloning is described in Example 1(1).

A genomic DNA coding for SPA-1 can be obtained by constructing a genomic DNA library from a target animal, and screening the genomic DNA library using cDNA, for example a full length cDNA obtained as described above. A concrete process for the screening is described in Example 3. For example, a genomic DNA coding for SPA-1 is obtained as a 5.7 kbp BamHI fragment (designated Spa-GC2) and a 6.6 kbp BamHI fragment (designated Spa-GC9) of the genomic DNA.

As shown in FIG. 5 as well as SEQ ID NO: 3, the 5.7 kbp DNA fragment (Spa-GC2) contains 4 exons (exons 1 to 4) which exist in a region of about 2.5 kbp of the 3′-terminal side of the 5.7 kbp fragment. On the other hand, the 6.6 kbp fragment (Spa-GC9) contains 12 dispersed exons (exons 5 to 16) (SEQ ID No:4). These exons 1 to 16 contain a full length of the above-mentioned cDNA. A coding region of the cDNA is contained in a region from the 3′-terminal half of the exon 5 to the 5′-terminal half of the exon 16.

According to the present invention, a DNA coding for SPA-1, or a fragment thereof such as Span-N or Span-C, can be obtained by treating the cDNA or genomic DNA prepared as described above with an exonuclease to eliminate an unnecessary portion, or cleaving the cDNA or genomic DNA with one or more appropriate restriction enzymes followed by supplementing a lacked portion with an oligonucleotide or eliminating a unnecessary portion. In addition, a gene coding for a polypeptide wherein one or more amino acids are lacked in the native amino acid sequence, one or more amino acids are added to the native amino acids sequence, and/or one or more amino acids in the native amino acid sequence are replaced with other amino acids can be obtained by subjecting said cDNA or genomic DNA to, for example, site-directed mutagenesis.

The present invention further includes DNA and RNA hybridizable with one of nucleotide sequences shown in SEQ ID NOs.: 1, 3 or 4. Such a hybridisable DNA or RNA preferably maintains a biological function of SPA-1, or a fragment thereof such as Span-N or Span-C. For example, the hybridisable DNA or RNA is that hybridisable with the above-mentioned cDNA or genomic DNA under the condition of, for example, 50% formamide, 5×SSC, 10% Na-dextran and 20 mM Na-phosphate (pH 6.5) at 42° C.

The present polypeptide or protein can be expressed in eukaryotic cells or prokaryotic cells according to a conventional procedure. The eukaryotic cells include cultured cells such as NIH3T3 cells, Cos-1 cells, CHO cells etc. of human or other animals, as well as enkaryotic microorganisms such as yeast, filamentous fungi. Yeast includes Saccharomyces cerevisiae) etc.; the filamentous fungi include the genus Aspergillus, such as Aspergillus niger etc. The prokaryotic organisms include bacteria. For example, Bacillus, such as Bacillus subtilis, Escherichia coli etc. are used.

To express said DNA in these hosts, an expression vector comprising a DNA containing said coding region, and an expression control region for said DNA is used. The expression control region used in the expression vector can be conventional one. For example, for expression in animal cells, a viral promoter such as LTR promoter, CMV promoter, SRα promoter etc. may be used; for expression in E. coli, T7 promoter, LacZ promoter etc. may be used; and as yeast promoter, for example, α-conjugation factor promoter can be used.

The present polypeptides or proteins can be obtained by culturing host cells transformed with an expression vector as described above, and recovering a desired polypeptide or protein from the culture. Transformation of host cells with an expression vector can be carried out depending on the nature of the host cells according to a conventional procedure. Culturing of the transformed cells also can be carried out according to a conventional procedure. Recovery and purification of a desired polypeptide from a culture are carried out according to a combination of conventional procedures used in purification of proteins including affinity chromatography, concentration, lyophilization etc.

EXAMPLES

The present invention is further explained in detail in the following Examples, but the scope of the invention is not limited to that of the Examples.

Example 1

Cloning and Characterization of SPA-1 cDNA

(1) Cloning of SPA-1 cDNA

According to the present invention, first, a gene which is little expressed in the quiescent state (G0/G1 phase) but induced in the cycling state (S phase) of lymphocytes, was cloned by differential hybridization between a lymphoid cell line (LFD-14) in the quiescent state by starvation of interleukin 2 (IL-2) for 3 weeks (LFD-14⁻) and those in the cycling state by restimulation of IL-2 (LFD-14⁺). A cDNA library was constructed using poly (A) ⁺RNA prepared from LFD14⁻ in a CDM8 cloning vector according to a conventional procedure (Aruffo, a., et al., Proc. Natl. Acad. Sci. USA, 84, 8573, 1987)). [α-³²P] dCTP-labeled cDNA probes were synthesized from poly (A) ⁺RNA's prepared from LFD-14⁻ and LFD-14⁺. Duplicate filters of the cDNA library were hybridized with each of above cDNA probes in hybridization buffer (5×SSC, 5×Denhardt's solution, 50 μg/ml salmon sperm DNA, 50 mM sodium phosphate, 0.1% SDS) at 65° C. overnight. Filters were washed with 0.1×SSC, 0.1% SDS at 65° C. before autoradiography. A cDNA clone, which was selectively detected by LFD-14⁺ probe, was designated SPA-1 and a vector comprising this cDNA was designated pcSPA-1. The SPA-1 cDNA can be isolated by cleaving said vector with a restriction enzyme Xho I.

(2) Structure of SPA-1 cDNA

The SPA-1 cDNA was sequenced according to a conventional procedure, and a result is shown in SEQ ID NO.: 1. This cDNA is about 3.5 kb in length, and has at the 5′-terminal side a long (about 1.2 kb) 5′-non-translation region containing a lot of short open reading frames (ORFs). This region is a strong translation-repressing region commonly found in certain oncogenes, showing that the SPA-1 gene is also strongly repressed at a level of translation.

This cDNA further comprises an open reading frame of about 2.1 kb starting from the 1200th nucleotide A (adenine) to the 3278th nucleotide C (cytosine) in SEQ ID NO.: 1. Among the amino acid sequence encoded by this open reading frame (SEQ ID NO:2), the N-terminal half (190 amino acid residues) (designated Span-N) has high homology with human Rap1GAP (GAP₃), and the C-terminal half (designated Span-C) has a novel sequence. The homology between the amino acid sequences of Span-N and GAP₃ is shown in FIG. 1.

(3) Preparation of Monoclonal Antibodies to Each Domain in SPA-1 N-terminal Portion

SPA-1 cDNA was cleaved with a restriction enzymes BglI and PstI to obtain a DNA fragment coding for Span-N and a DNA fragment coding for Span-C (about 140 amino acid residues). On the other hand, pGEX-1 vector (Pharmacia) was cleaved with PstI, blunt-ended using T₄ polymerase and EcoRI linkers were added to the blunted ends. The above-mentioned Span-N DNA fragment or Span-C DNA fragment was inserted into the EcoRI sites of the modified pGEX-1 vector to construct an expression plasmid pGEX-SpanN or pGEX-SpanC comprising a sequence coding for a fusion protein of the Span-N or Span-C and GST (glutathione-S-transferase), respectively. These expression plasmids were expressed in E. coli, and expression products were recovered and purified to obtain Span-N/GST fusion protein and Span-C/GST fusion protein respectively.

Then 200 μg of the fusion protein was mixed with Freund's complete adjuvant and the mixture was subcutaneously administered to immunize an Arumenia hamster (male, 5 weeks old). After that, 200 μg each of the fusion protein mixed with Freund's incomplete adjuvant was three times intraperitoneally administrated to the hamster, at intervals of two weeks. After three days from the final immunization, the spleen was removed from the hamster, and minced to prepare a single cell suspension of the spleen. This suspension was subjected to a cell fusion with mouse myeloma cell line P3U1, according to the Leo, 0 et al. method (Proc. Natl. Acad. Sci. USA, 84: 1374, 1984), to obtain hybridomas.

Among the hybridomas, clones producing a desired antibody were selected with ELISA using corresponding fusion protein used to immunize the hamster. Namely, 1 μg/well of each fusion protein (GST-SpanN, or GST-SpanC) or 1 μg/well of GST protein alone was immobilized to a 96-well plate, and 100 μl of hybridoma supernatant was added into each well and allowed to react with the immobilized protein.

Then, anti-hamster IgG-peroxidase was added to the wells for reaction, followed by a substrate ABTS (2,2′-adino-di-3-ethyl-benzothianodino-6-sulfate) for coloring, and clones which react with the fusion protein but do not react with GST were selected as positive clones. Cells in the positive wells were cloned by limiting dilution method to obtain a clone from a single cell. A monoclonal antibody against Span-N is designated “F6”, and monoclonal antibody against Span-C is designated “H10”. FIG. 7 shows reactivity of each monoclonal antibody with fusion proteins, analyzed by Western blotting.

Namely, FIG. 7 shows a result obtained by the following method: 10 μg of GST-SpanN or GST-SpanC fused protein, or GST alone was separated by SDS-PAGE, blotted on a membrane, reacted with an F6 or H10 antibody solution (10 μg/ml), and detected with ¹²⁵I-Protein A (Amersham).

Note, the hybridoma producing monoclonal antibody F6 was designated F6 and deposited with National Institute of Bioscience and Human-Technology Agency of Industrial Science and Technology as FERM BP-4839 on Oct. 18, 1994 under the Budapest treaty; and the hybridoma producing monoclonal antibody H10 was designated H10 and deposited with the National Institute of Bioscience and Human-Technology Agency of Industrial Science and Technology as FERM BP-4840 on Oct. 18, 1994, under the Budapest treaty.

(4) Detection of SPA-1 Protein by Monoclonal Antibody

Protein was extracted from cultured cells of lymphoid cell line LFD14 (Kubota, H. et al., J. Immunol. 145, 3924, 1990) according to a method of Harlow, E. et al., Mol. & Cellular Biology 6: 1579, 1986), and identified by immunoblotting using said monoclonal antibodies, immunoprecipitation method, immunostain method etc.

As a result, for example, a protein from lymphoid cell line LFD14 was detected as a band of a molecular weight of about 68 KDa in Western blotting using monoclonal antibody F6. From this result, it is expected that the SPA-1 gene encodes a nuclear protein of about 68 KDa.

Namely, it is expected that SPA-1 protein of the present invention has an amino acid sequence starting from the first amino acid methionine and ending at the 693rd amino acid alanine in SEQ ID NO: 1.

Example 2

Expression of SPA-1 cDNA

(1) Expression of SPA-1 Protein

Expression by in vitro transcription/translation

FIG. 8 shows a result of an analysis of SPA-1 protein expressed by in vitro transcription/translation method using various lengths of SPA-1 cDNA as a template. As shown in FIG. 8, pBluescript Ks⁺-SPA-1 plasmid containing a full length SPA-1 cDNA, clones (#52, #35, #33, and #92) lacking 5′-terminal portion of said SPA-1 cDNA in different length, and plasmids containing a full length ORF but lacking 5′-non-translational region which negatively acts on the translation upwards from the different positions (NcoI (1928), BalI (2229), EcoRI (2879), or DraI (3035)) downstream of the plasmid #35 were used as a template.

Using 10 μg of these template DNAs, complementary mRNAs (cRNAs) were synthesized with an RNA transcription kit (Stratagene). These cDNAs were in vitro translated in the presence of ³⁵S-methionine (Amersham) according to the Tagawa et al. method (J. Biol. chem. 256: 20021, 1990) using an in vitro expression translation kit (Promega). The translation product was immunoprecipitated with the above-mentioned H10 antibody and protein A beads (Pharmacia), and the precipitate was analyzed by SDS-PAGE.

As a result, where full length pBluescript-KS⁺-SPA-1, #52 and #35 plasmids completely containing ORF and 3′-non-translational region were used as templates, a specific band of about 85 KDa was detected, while where plasmid (#33) lacking a part of the ORF was used a translation product shortened (about 50 KDa) corresponding to the lack of the ORF was detected. In addition, where plasmids (#35/BalI, #35/EcoRI, and #35/DraI) lacking 3′-non-translation region were used, translation products shorter than 85 kDa corresponding to an extent of lacking were obtained.

These results show that the SPA-1 protein is a polypeptide starting from the first amino acid methionine and ending at the 693rd amino acid alanine encoded by a nucleotide sequence started with the 1200th nucleotide A and ending at the 3278th nucleotide C in SEQ ID NO: 1.

Expression by stable animal cell transfectant

The SPA-1 cDNA was obtained by cleavage of plasmid SPA-1 with restriction enzymes BglI and DraI, and inserted into EcoRI site of pSRa expression vector (Takebe, Y. et al., Mol. Cell Biol., 8: 466-472, 1988) to construct an expression plasmid SRα-SPA-1, which was then co-introduced into NIH3T3 cells (ATCC CRL-1658) together with a plasmid pSV₂NeO and transfected cells were selected by G418 to obtain a stable transfectant (NIH/SPA-1 cells).

As shown in FIG. 9A, the NIH/SPA-1, cells grew under a usual culture condition (supplemented with 5% serum) in a manner not different from control cells, i.e., NIH3T3 cells to which SRα vector alone had been introduced do. However if the same cells were cultured in a serum-reduced condition (0.5% serum) to synchronize them to the G1 phase (extended G1) and after a certain time later the cells were restimulated with serum to reenter the cell cycle, they rapidly died off in the middle to end of the S phase (FIG. 10A). Morphologically, the cells became round up, and remarkable nuclear condensation was observed, and therefore it was considered that so-called mitotic catastrophes occurred (FIG. 9B). In addition, SPA-1 exhibits a unique change of expression along with synchronization of cell cycle, suggesting that expression thereof, similar to cyclines, is controlled by cell cycle (FIGS. 10, B and C).

FIG. 9 shows induction of the death of cells by growth stimulation after blocking the G₁ phase of cell cycle, in NIH3T3 cells (NIH/SPA-1) transfected with SPA-1 cDNA. FIG. 9A shows a result obtained by culturing the NIH/SPA-1 cells () and the NIH-SRα cells (∘) prepared by introducing pSRα vector alone into NIH3T3 cells in the presence of 5% serum to an almost confluent state, transferring the cells to a medium containing 0.5% serum, and after culturing the cells for 0, 24 or 48 hours, transferring the cells to a medium containing 20% serum so as to count the number of cells as time elapses.

FIG. 9B shows micrographs of NIH/SRα cells and NIH/SPA-1 cells cultured in the presence of 0.5% serum for 48 hours and then in the presence of 20% serum for 18 hours. The right shows the morphology of the nucleus of the cell at that time, in Hoechst 33427 (Sigma). The shrink of the nucleus was observed in NIH/SPA-1.

In FIG. 10, A shows a result of analysis of cell cycle in NIH/SPA-1; the upper portion relates to NIH/SRα cells and the lower portion relates to NIH/SPA-1 cells. After 16 hours from the addition of serum, NIH/SPA-1 cells had died (control cells had entered to the S phase). FIG. B shows an accumulation of SPA-1 protein in a serum-free culture (G₁ arrest). For NIH/SPA-1 cells, although the transfected SPA-1 mRNA was detected, under a usual condition (lane of oh) SPA-1 gene was not substantially detected by Western blotting (probably due to constant degradation). However, where a serum concentration was reduced to 0.5% to maintain the cell cycle at the G₁ phase (G₁ arrest), accumulation of SPA-1 protein was observed.

FIG. 10C shows the kinetic change of SPA-1 protein after the addition of serum. After the G₁ arrest for 48 hours, the cell cycle was started by the addition of serum, then only living cells were recovered at each time and SPA-1 protein was detected. A part of NIH/SPA-1 cells survived after the addition of serum for 24 hours, and in these cells the increase of cαc2 expression was observed. On the other hand, at this point, SPA-1 protein had already decreased.

Expression of recombinant SPA-1 in E. coli

The SPA-1 cDNA was cleaved with a restriction enzyme BglI (which cleaves at the 1171st nucleotide) and a restriction enzyme DraI (which cleaves at the 3038th nucleotide) to obtain a BglI-DraI fragment, which was then blunt-ended with T4 polymerase. This DNA fragment was ligated to EcoRV-cleaved plasmid BS-SK (Transgene) to obtain a plasmid SK⁺-SPA-1. Next, this plasmid was cleaved with Hind III, and to the resulting Hind terminals were added BamHI linkers, and the BamHI linkers were cleaved with BamHI to obtain a BamHI fragment, which was inserted into BglII-digested expression plasmid pET-16b (Novagen, USA) to obtain an expression plasmid pET-SPA1. This plasmid was used to transform E. coli.

By culturing the E. coli, subjecting an expression product from the culture to electrophoresis, and detecting the product by the above-mentioned monoclonal antibody F6, a band corresponding to a molecular weight of 85 KDa was detected and expression of recombinant SPA-1 (rSPA-1) was confirmed.

A process for construction of the expression plasmid pET-SPA-1 is shown in FIG. 3.

(2) Physiological Activities of Span-N

Since Span-N has homology with GAP3, GAP activity of the above-mentioned GST-SpanN fusion protein was tested. As a control, a fusion protein of human GAP3 (75th to 663rd amino acid residues) and GST was used. The effects of these fusion proteins on GTPase activity of yeast Rsr1 (1st to 272nd residues), human Rap1A (Glu⁶³) (1st to 184th residues), human Ha-Ras (1st to 189th residues) and a human RhoA (1st to 193 residues) GST fusion protein (Nur-E-Kamal et at., Mol. Biol. Cell 31, 1437-1442, 1992; Nur-E-Kamal et al., J. Biol. Chem. 267, 1415-1418, 1992) was investigated according to the Maruta et al. method (J. Bio. Chem. 266: 11661-11668, 1991). As a result, it was shown that although the Span-N was not effective to Ha-Ras, Racl, Rhol etc., it has selective GAP activity to Rap1 and Rsr1.

TABLE 1 Activation of GTPase activity of Rsr1, Rap1, etc. by Span-N or GAP3m Native GTPase activity Stimulation (times) smG Protein (Turn over/min.) Span-N GAP3m Rsr1 0.001 16.0 7.0 Rap1A(Glu⁶³) 0.0015 6.0 10.0 Ha-Ras 0.022 0.3 0 RhoA 0.060 0.6 0 Rac1 0.090 0

In addition, the relationship between Span-N concentration and Rsrl GTPase activity is shown in FIG. 4. The Figure shows that Rsr GAP activity of Span-N depends on its concentration. Note that GAP activity was measured according to the Maruta et al. method (J. Biol. Chem. 266: 11661-11668, 1991).

SPA-1 is a nuclear protein, while there is no report that Rap1 exists in the nucleus. Therefore, activity of Span-N etc. to the sole low molecular weight G protein, Ran, known to be present in nucleus was studied. As a result, it was shown that Span-N exhibits a clear GAP activity on Ran. This result is shown in Table 2.

TABLE 2 Activation of Ran GTPase by Span-N and other GAPSs GAPs EC₁₆ (μg/ml) SPA-1(Span-N) 25 GAP3m(Rap GAP) 130 p190C(Rho GAP) 150 NF1-GDR(Ras GAP) 300

In addition, FIG. 5 shows the relationship between Span-N concentration and Ran GTPase activity.

Example 3

Cloning of Genomic Gene

(1) A mouse genomic library (EMBL3-Adult DBA/2J liver DNA:CLONTECH, ML 1009d) comprising 1.0×10⁶ clones was blotted on Hybond-N⁺ membranes (Amersham, RPN 303B). A vector SPA-1 cDNA/pBluescript incorporating a SPA-1 cDNA was cleaved with XhoI (Toyobo, XHO-101) to obtain a full length SPA-1 cDNA, which was then labeled with α³²P-dCTP (Amersham, PB0205) using a Nick Translation Kit (Amersham, N5000).

This probe was reacted with the above-mentioned genomic library in the presence of Rapid Hybridization Buffer (Amersham, RPN1636). As a primary screening, 15 positive or pseudopositive signals were obtained. As a secondary screening 9 positive clones were obtained. These were further screened so as to confirm all of the 9 strains were cloned. Genomic DNA in these clones are designated GC1 to GC9, respectively.

(2) Preparation of Mouse Total DNA

First 2 cm of the tail of a Bal b/c mouse of 4 weeks old was cut off, and was put into 1.5 ml Epptendolf tube. Then the cut tail was sliced with scissors. In this tube were added 500 μl of a mixed solution (439 μl of 1×SSC, 5 μl of 1M Tris-HCl (pH 7.5) and 1 μl of 0.5M EDTA (pH 8.0)), 50 μl of 10% SDS, and 5 μl of 20 mg/ml proteinase K, and the mixture was incubated at 37° C. for 12 hours.

Next, 500 μl of buffered phenol was added thereon, and the whole was gently mixed for 5 minutes. The mixture was centrifuged at 10,000 rpm, at a room temperature for 5 minutes. The liquid phase was transferred into a fresh Epptendorf tube, and 700 μl of isopropanol was added thereon, and the tube was reversed a few times to generate fibrous precipitate.

This precipitate was transferred to a fresh tube into which 500 μl of 70% ethanol had been introduced, and after removing the 70% ethanol, the precipitate was washed with 100% ethanol. The precipitate was dried with dry air and 100 μl of TE buffer was added thereon to prepare a total DNA.

(3) Screening of Genomic DNA Coding for SPA-1

The total DNA prepared in the section (2) was cleaved with BamHI (Toyobo, BHA 102) or EcoRI (Toyobo, ECO-101), blotted on Hybond-N⁺ membranes, and screened by hybridization with the full length SPA-1 cDNA probe prepared in the above section (1). The hybridization was carried out in Rapid Hybridization Buffer as described in the section (1).

As a result, 5.7 kb and 6.6 kb BamHI fragments as well as 9.2 kb, 5.2 kb and 1.4 kb EcoRI fragments were positive. The 5.7 kb and 6.6 kb BamHI fragments contained a full length of SPA-1 cDNA and corresponded to the above-mentioned genomic fragments Spa-GC2 and Spa-GC9. Phage vectors comprising these genomic fragments were designated Spa-GC2/EMBL-3 and Spa-GC9/EMBL-3, respectively.

(4) Sequencing

These viral vectors were prepared and cleaved with BamHI, and using a Gene Clean Kit (Funakoshi) a 5.7 kb BamHI fragment from Spa-GC2/EMBL-3 and a 6.6 kb BamHI fragment from Spa-GC9/EMBL-3 were prepared respectively.

Next, each of these fragments was inserted into pBluescript II SK(+) (Toyobo SC212205) at its BamHI site using a DNA Ligation Kit (Takara 6021) and subcloned. Then deletion mutants were prepared by Kilo-Sequence Deletion Kit (Takara, 6030), and sequencing was carried out using a 7-deaza Sequenase (Toyobo, US 70777). As a result, it was founded that the Spa-GC2 contains exons 1 to 4 in its 3′-terminal half, and the Spa-GC9 contains dispersed exons 5 to 16.

Exon 1 extends from base pair number 3109 through base pair number 3284 of SEQ ID NO:3. Exon 2 extends from base pair number 3764 through base pair number 4555 of SEQ ID NO:3. Exon 3 extends from base pair number 5147 through base pair number 5273 of SEQ ID NO:3. Exon 4 extends from base pair number 5354 through base pair number 5524 of SEQ ID NO:3.

The nucleotide sequence of Spa-GC2 is shown in SEQ ID NO.: 3, and the nucleotide sequence of Spa-GC9 is shown in SEQ ID NO.: 4. In the Spa-GC9, an amino acid coding region in cDNA is contained in a region from the 3′-terminal half of the exon 5 to the 5′-terminal half of the exon 16(SEQ ID NO: 5).

Note that FIG. 6 shows relative positions of the genomic fragments including Spa-GC2 and Spa-GC9.

It was suggested that the SPA-1 protein participates in the regulation of DNA replication and cell division because the protein strongly expressed after the S phase in the cell cycle of normal lymphocyte. On the other hand, it was shown that the said protein contains a Ran GAP activity domain at its N-terminal portion. The Ran is the sole low molecular weight G protein present in the nucleus and is associated with RCC-1 which is a GDP-GTP exchanger of Ran GTPase. RCC-1 is a nuclear protein well conserved in all cells from yeast to mammal, and is well known as a protein participating in check mechanism of entering into the G₂/M phase (namely, prevention of premature cell division prior to completion of DNA replication). In addition, recently it has been found that the RCC-1 gene precipitates in various aspects of cell nucleus functions including initiation of DNA replication, extranuclear transport of RNA, etc.

The RCC-1/Ran system is, however, constitutionally expressed regardless of the cell cycle. Accordingly, for long time, an intervention of a cell cycle-dependent factor, especially GAP molecule as an entity which links the cell cycle and RCC-1/Ran is expected. However, its true entity has not been clear. The finding in the present invention strongly suggests that SPA-1 is in fact the intervenient entity. In addition, it was found in the present invention that an over-expression of SPA-1 causes the mitotic catastrophes. This finding suggests that SPA-1 is a central molecule responsible for cell cycle-dependent control of the RCC-1/Ran system.

A mechanism by which the SPA-1 micro-regulates the RCC1/Ran system which represses cyclin/cdc 2 system driving DNA synthesis and cell division is an important object to be solved in future. Especially, the fact that the SPA-1 is highly expressed in lymphoid cells having unique cell growth properties suggests that the SPA-1 plays an important role in a growth control of the lymphoid cells and checking mechanism thereof.

Accordingly, the present protein is promising as differentiation control agent of lymphocytes. In addition, the present protein may be useful as an anti-tumor agent because if the present protein is expressed in tumor cells, it may induce the death of cells at the S phase of the cell cycle. 

What is claimed is:
 1. An isolated DNA coding for a cell division mechanism controlling protein which is not expressed during interphase (G₀/G₁) of the cell cycle but is expressed in the nucleus during cell division, wherein said DNA hybridizes with a nucleotide sequence complementary to SEQ ID NO: 1 in the presence of 50% formamide and 5×SSC at 42° C.
 2. An expression vector comprising a DNA according to claim
 1. 3. A host transformed with an expression vector according to claim
 2. 4. A process for production of a cell division mechanism controlling protein, comprising the steps of: culturing a host according to claim 3, and recovering the protein from the culture.
 5. An isolated DNA coding for a cell division mechanism controlling protein consisting of the amino acid sequence from the first Met to the 693rd Ala of SEQ ID NO:
 2. 6. An expression vector comprising a DNA according to claim
 5. 7. A host transformed with an expression vector according to claim
 6. 8. A process for production of a cell division mechanism controlling protein, comprising the steps of: culturing a host according to claim 7, and recovering the protein from the culture.
 9. An isolated DNA coding for Span-N protein consisting of the amino acid sequence from the first Met to the 190th Leu of SEQ ID NO:
 2. 10. An expression vector comprising a DNA according to claim
 9. 11. A host transformed with an expression vector according to claim
 10. 12. A process for production of Span-N protein, comprising the steps of: culturing a host according to claim 11, and recovering the protein from the culture.
 13. An isolated DNA coding for Span-C consisting of the amino acid sequence from the 191st Ala to the 327th Leu of SEQ ID NO:
 2. 14. An expression vector comprising a DNA according to claim
 13. 15. A host transformed with an expression vector according to claim
 14. 16. A process for production of Span-C protein, comprising the steps of: culturing a host according to claim 15, and recovering the protein from the culture.
 17. An isolated genomic DNA coding for a cell division controlling protein wherein the genomic DNA consists of the 904th nucleotide to 5741st nucleotide of SEQ ID NO:
 4. 18. An expression vector comprising a DNA according to claim
 17. 19. A host transformed with an expression vector according to claim
 18. 